The present invention relates to a method and apparatus for manufacturing plural component materials and, more particularly, to a method and apparatus for forming rigid urethane structures from reactive components.
Urethane elastomer materials are commonly manufactured by combining a first reactive component, such as isocyanate, with a second reactive component, such as polyol resin. Each of the components is, by itself, generally stable if properly stored; however, when they are mixed under the proper conditions, they initiate a chemical reaction that causes the components to polymerize and form the urethane structure.
Usually, cross-linking and curing of the plural component urethane materials are substantially completed in a matter of minutes. Therefore, it is not practical to mix the components in advance and then apply the mixture from a conventional dispensing device since the components would tend to cross-link and cure before dispensing could be effected. Accordingly, it is necessary to maintain the components separate from one another until the last possible moment and to mix them in the dispensing device itself as close as possible to the location where the mixture is to be dispensed from the device.
One current system especially developed to process reactive urethane components comprises a hand-sprayed rim (reaction-injection molding) machine designed to operate at high pressures of from about 1400-1600 psi.
Basically, this equipment includes an isocyanate supply tank and a polyol supply tank for storing supplies of the components to be mixed. A transfer pump is connected to the output of each tank to transfer the components to proportioning pumps which, in turn, are provided to deliver each component to a mixing and dispensing device (i.e., a spray gun) at the desired rate. Each tank is provided with a tank heater to initially heat the components to the desired temperatures for effective polymerization and to maintain the materials at the proper viscosities for reliable flow of the components through the system.
The proportioning pumps are hydraulically operated reciprocating pumps and function to deliver the components to the spray gun to be mixed therein in the correct proportion. From the proportioning pumps, the components flow through heat exchangers and heated hoses to the spray gun. Heating of the components within the hoses is necessary to ensure that the components are maintained at the proper temperatures inasmuch as during normal operation of the system, component materials may remain in the hoses for substantial periods of time between dispensing operations and, thus, could cool significantly if the hose heaters are not provided.
In the spray gun, the components are mixed together and ejected from the outlet orifice of the spray gun. High-pressure air helps to atomize the mixed components and assists in cleaning the mixture from the spray gun.
Although the currently known equipment, as described above, is generally effective and reliable in manufacturing rigid urethane elastomer structures, it is not fully satisfactory for a number of reasons.
The system's means to deliver the plural components to the spray gun is costly and includes independently operating hydraulic drive means for the pumps and independently controlled heated hoses leading from the pumps to the spray gun. The delivery ratios and the delivery temperatures of the two components are thus subject to variation, requiring close attention of the operator. For example, the temperature and viscosity of the components reaching the spray gun are each dependent upon the time they reside within the heated hoses, which is dependent upon the spray gun operator, the heated hose controls, and pump drives. Furthermore, the proportioning pumps are both costly and relatively complex and require complete hydraulic power systems including oil pumps and complete oil-circulating systems to drive the proportioning pumps.
The system also includes separate, storage tanks for storing relatively small quantities, e.g., five to fifteen gallons, of isocyanate and polyol resin. These tanks increase the cost of the system and must be periodically refilled from 55-gallon drums in which the materials are normally shipped and stored.
In addition, the system requires a plurality of heating apparatus and controls including storage tank heaters to initially heat the components within the storage tanks, heat exchangers in the fluid delivery system to heat the components to the desired temperature to be delivered to the mixing and dispensing device, and heated hoses in both the isocyanate and polyol lines to maintain the components at the proper temperatures during periods when they remain within the hoses between dispensing operations.
Thus the system is complex and costly and subject to variability in performance due to its operation by an operator and variance in the operation of its components.